A theoretical study of the lowest2B1,2A1and2B2electronic states in H2S+and a comparison with corresponding states in related systems

Large scale configuration interaction calculations are employed to study the potential energy surfaces of the three lowest lying states in H2S+. The calculated structural data for the X 2 B 1 and A 2 A 1 states are in very good agreement with previous evidence, but the 2 B 2 state is found to exhibit an [S---H2]+ structure with large SH bond separations and a very small internuclear angle of 32°. Energies and wavefunctions are calculated for all three vibrational modes in the X 2 B 1 and A 2 A 1 excited states of H2S+ and D2S+ and the corresponding Franck-Condon factors for the A 2 A 1-X 2 B 1 band are determined; a maximum in absorption intensity is predicted to occur for v′2 = 5–6 in H2S+ and for v′2 = 7–8 in D2S+ for the A 2 A 1-X 2 B 1 transition, for which the calculated T 0 energy of 18 620 cm-1 is in excellent agreement with the experimentally determined value of 18 520 cm-1. Extensive comparison is made with the other AH2 systems PH2, NH2 and H2O+ and trends with respect to geometry, vertical excitation and ionization energies as well as vibrational structure are pointed out; for this purpose the 2 B 2 potential energy curve of PH2 has also been calculated.